Semiconductor devices are used in a variety of electronic applications, such as, for example, personal computers, cell phones, digital cameras, and other electronic equipment. Semiconductor devices are typically fabricated by sequentially depositing insulating or dielectric layers, conductive layers, and semiconductor layers of material over a semiconductor substrate, and patterning the various material layers using lithography to form circuit components and elements thereon.
The semiconductor industry continues to improve the integration density of various electronic components (e.g., transistors, diodes, resistors, capacitors, etc.) by continual reductions in minimum feature size, which allow more components to be integrated into a given area. In some devices, multiple dies or packages with active devices or circuits are stacked vertically to reduce the footprint of a device package and permit dies with different processing technologies to be interconnected. Interconnections for this vertical stacking are created on the top and bottom surfaces of a substrate by forming redistribution layers (RDLs) with conductive lines in insulating layers. The RDLs, and the dies external to a particular package, are electrically connected to dies in a package, or dies on opposing sides of the package by vias extending through the substrate. The external packages are electrically connected to the RDL by conductive connectors disposed on lands exposed at the surface of the RDLs. Vias disposed in a substrate connect RDLs on opposite sides of a package.